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global keyword and $GLOBALS usage in PHP

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Release： 2016-08-08 09:19:33

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<?php $a = 1; /* global scope */ function Test () { echo $ this script will not have any output because The echo statement refers to a local version of the variable $a, and within this scope, it is not assigned a value. You may notice that PHP's global variables are a little different from C language. In C language, global variables automatically take effect in functions unless overridden by local variables. This may cause some problems, someone may accidentally change a global variable. Global variables in PHP must be declared as global. global Keyword First, an example using global:

Example #1 Using

global

= 1

;$b

function

Sum(){ global $a, $b; + $b; } Sum (); echo $b;?> After global variables $a and $b are declared in a function, all references to either variable will point to its global version. PHP has no limit on the maximum number of global variables that a function can declare. The second way to access variables in the global scope is to use special PHP customization $GLOBALS Array. The previous example could be written as: Example #2 using $GLOBALS replacementglobal <?php$a =

;

$b = 2 ;

function

Sum( ){

$GLOBALS['b'] =

$GLOBALS

['a' ] + $GLOBALS [ 'b' ];}Sum(); echo $b; ?>$GLOBALS is an associative array, each variable is an element, the key name corresponds to the variable name, and the value corresponds to the content of the variable. $GLOBALS Exists in the global scope because $GLOBALS is a superglobal variable. The following example shows the use of superglobal variables: Example #3 Example demonstrating super global variables and scope <?php function test_ global(){ / / Most of the predictions Defining variables is not "super", they need to use the 'global' keyword to make them available in the local scope of the function.

global

$HTTP_POST_VARS; echo $HTTP_POST_VARS[

'name'

];

// Superglobals are valid in any scope, they do not require 'global ' statement. Superglobals were introduced in PHP 4.1.0. echo $_POST['name'];} ?> The above introduces the usage of the global keyword and $GLOBALS in PHP, including relevant content. I hope it will be helpful to friends who are interested in PHP tutorials. 